1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof. More particularly, the present invention relates to a semiconductor device and a manufacturing method thereof characterized in a connection portion between a lower wiring or a semiconductor element portion and an upper wiring.
2. Description of the Related Art
The diameters of a contact hole and a through hole are reduced as a semiconductor device is integrated. Further, a wiring width is reduced.
In an integrated circuit, a transistor must be electrically connected to lower and upper wirings in a wiring section or a multilayer wiring structure. In a general semiconductor device, contact and through holes are formed in a layer insulating film. The transistor and the upper and lower wirings are connected to each other through these contact and through holes. In a connection portion of the transistor and the upper and lower wirings, as shown in FIG. 1a, the width of an upper wiring 4 is set to be wider than a diameter of each of a contact hole and a through hole 2 so as to prevent the upper wiring 4 from being cut at connecting stages, etc.
However, as the diameters of the contact and through holes are reduced and the wiring width is reduced, wirings are cut at connecting stages in contact and through hole portions in many cases, thereby reducing reliability in wiring.
In one method for improving wiring reliability in the connection portion, a buried conductive material is formed in each of the contact and through holes to reduce a step difference between wirings in the connection portion. For example, such a method is proposed in Japanese Patent Publication (KOKOKU) No. 410219 and Japanese Patent Application Laying Open (KOKAI) No. 4-17329. In Japanese Patent Publication (KOKOKU) No. 4-10219, tungsten is selectively grown in an opening of an insulating film formed on a silicon substrate so that this opening is buried by this tungsten. Thus, the insulating film is flattened and an aluminum wiring is formed on this insulating film. In Japanese Patent Application Laying Open (KOKAI) No. 4-17329, a first aluminum film is formed in a substrate opening portion by a selective growing method so that a surface of the substrate opening portion is flattened. Thereafter, energy particles are irradiated onto a surface of an insulating film so that an aluminum film is also grown on the insulating film, thereby forming a second aluminum film.
These methods for burying each of the contact and through holes by a conductive material are useful to improve wiring reliability. Further, there is no fear of cutting wirings at connecting stages in these methods. Accordingly, as shown in FIG. 1a, it is not necessary to widen the wiring width in only the connection portion. Therefore, it is possible to reduce distances between adjacent wirings so that it is useful to reduce the size of a semiconductor element.
However, as the diameters of the contact and through holes are reduced and the wiring width is reduced, a new problem is caused when a position of the upper wiring is shifted from each of the contact and through holes. For example, this problem will be described with respect to the through hole and the upper wiring. When the through hole has a square shape having 0.4 .mu.m on one side thereof and the width of the upper wiring is set to 0.4 .mu.m and there is no shift in position between the through hole and the upper wiring 4 as shown in FIG. 1b, a contact surface between the upper metallic wiring 4 and a buried metal is equal to a surface area provided by a diameter of the through hole. However, if there is a shift in position between the upper wiring and the through hole and this shift is equal to 0.2 .mu.m for example, the contact area between the upper wiring 4 and the buried metal is reduced by 50% as shown in FIG. 1c in comparison with the case in which no position shift is caused. Accordingly, when an electric current flows through the through hole, there is a fear of fusion or melting, etc.
When the buried conductive material and an upper wiring material are constructed by the same material as shown in Japanese Patent Application Laying Open (KOKAI) No. 4-17329 and the position shift is caused, the buried conductive material is also etched when a pattern of the upper metallic wiring is formed by etching. Accordingly, reliability of each of the contact and through holes is greatly reduced.